High frequency ignition system



Sept. 1, 1959 H. B. HOLTHOUSE HIGH FREQUENCY IGNITION SYSTEM 3 Sheets-Sheet 1 Filed July 11, 1955 m w m m I n i l m I I P 1959 H. B. 'HOLTHOUSE 2,902,527

HIGH FREQUENCY IGNITION SYSTEM Filed July 11, 1955 s Shets-Sheet 2 IN V EN TOR. Hmm Y 5, H01. 7710055 //'.12 BY :2 gm

Sept. 1, 1959 H. B. HOLTHOUSE HIGH FREQUENCY IGNITION SYSTEM Filed July 11, 1955 I5 Sheets-Sheet 3 I05 I02 I03 INVENTOR. Ham? y 6. H01. 77/04/55 Uite Stats 1 This invention relates to a high frequency ignition system, particularly to an ignition system operable from a magneto and having a high frequency oscillating primary circuit.

Conventional ignition systems for internal combustion engines generally embody a low frequency spark coil ignition circuit and a mechanical make and break arrangement synchronized with the piston of the engine to provide for proper timing of the spark. Various automatic mechanical means are utilized for advancing or retarding the time of sparking at the spark plug to give the engine suitable running characteristics at different speeds. Such systems generally require an impulse coupling to supply an adequate source of current during periods of low engine speed and during starting because the current output of a magneto or generator at low engine speeds may be of insufiicient voltage to cause adequate sparking at the spark plugs.

Ignition systems have also been employed involving the formation of a high frequency oscillating current which is conducted through the primary coil of a high frequency transformer and serves to generate in the secondary coil of the transformer a current of high frequency and high potential. This latter current is caused to spark at the spark plugs and produces a spark of highly desirable characteristics since it is characterized both by high frequency oscillation and by high potential.

Such systems are also advantageous, especially when operated from a magneto, because they alford the possibility of so-called wave-form timing in place of mechanical timing with its attendant known difficulties. In a typical circuit embodying wave-form timing, the primary coil of a high frequency transformer is connected in series with a suitable condenser or capacitor and a very short spark gap, often referred to as a micrometer spark gap, and not to be confused with the ignition spark gap. The condenser is charged by current from a mag neto designed to give a current of suitable wave-form characteristics synchronized with the pistons of the engine. In operation, the magneto current charges the condenser until a potential is built up to cause sparking at the micrometer spark gap giving rise to a high frequency oscillating current in the primary coil of the high frequency transformer. This, in turn, induces a current of high potential in the secondary coil of the transformer which furnishes the spark for firing the combustion mixture in the combustion chamber of the engine.

Ignition systems employing wave-form timing and a high frequency oscillating primary circuit can, with proper modification for low speed operation and starting, dispense with the conventional make and break arrangement for firing the combustion mixture. The actual speed of the magneto which will charge the condenser sufiiciently to cause sparking across the micrometer spark gap need only be very low because of the extremely short micrometer spark gap which can be employed. Generally the revolution of the engine at the l atented Sept. 1, 1959 rate of a very few revolutions per minute will cause the circuit to function and the spark plugs to fire. Such ignition systems are well adapted to use with two-cycle and four-cycle engines of low power output, such as outboard motors, gasoline-powered tools and other portable engines, where the elimination of batteries of all sorts is highly desirable. Such systems are, however, also highly advantageous when used with higher powered engines such as aircraft, automobile and stationary engines, even though accumulators may be required to furnish the mechanical power for starting, for lighting and for operating numerous other services about the vehicle or premises.

Although high frequency ignition systems of the general type just described have the known advantages pointed out, they have, as heretofore utilized, possessed certain disadvantages inherent in their mechanical arrangement which have limited seriously their ruggedness and unchanging characteristics over long periods of use. These difiicultics have centered principally around the micrometer spark gap and the maintenance of its sparking characteristics constant over long periods of high speed operation of the engine. The difficulty of this problem is apparent when it is realized that with slow speed operation or during starting of the engine the voltage buildup across the micrometer spark gap may, at best, be low. Consequently, if the gap is too long, the engine will fail to start or will stop if already running. For this reason it is desirable that the length of the micrometer spark gap be of the order of a very few thousandths of an inch, or even less. Furthermore, for even firing of the engine, the length of the gap must be precisely the same for each discharge of the condenser across the gap. The time of sparking and, therefore, of firing in the combustion chamber, depends, not only upon the rate of charging of the condenser by the charging current, but, also, upon the constancy of the micrometer spark gap so that sparking will occur at precisely the same critical value of the charge on the condenser over long periods of operation. Even the smallest speck of dirt lodged within the gap will influence the firing time. The difiiculty of maintaining such a short gap free of dirt is apparent.

The problem is further complicated by the fact that, when sparking occurs at the gap, the air Within the gap is ionized to some extent and this ionization persists from one sparking to the next, thus causing the succeeding sparking to occur prematurely because of the reduced resistance to the passage of the spark caused by the increased conductivity of the ionized air within the gap. Consequently, unless some provision is made to purge or clean the gap between sparkings to remove all ionized air and foreign material, very uneven firing will result, especially at higher engine speeds. Such a gap is said to be unstabilized.

Various expedients have been proposed for overcoming these difficulties so that the micrometer spark gap will be in precisely the same condition as regards the distance separating the electrodes and the absence of ionized air and foreign material between them on each occasion when sparking is to occur across the gap. A micrometer spark gap, in this condition, is said to be stabilized between succeeding sparkings. One of the proposed methods for stabilizing a micrometer spark gap comprises enclosing the gap in a small chamber through which a current of air is caused to pass in a direction across the gap. In one modification this is accomplished by providing the small chamber enclosing the gap with a porous wall or with a wall with a port in it and connecting a port in the opposite wall with the intake manifold of the engine by suitable conduits. Although this method has proved of some value, it has not solved the problem completely or satisfactorily be cause, among other reasons, the flow of air through the chamber, as well as the actual air pressure in the chamber, depends to a considerable extent upon the speed of the engine and the pressure in the intake manifold. Thus the ventilation in the micrometer spark gap is variable and, furthermore, any small particles of foreign matter which do lodge in the gap are not generally removed in the more or less uniform stream of air pass ing through the gap.

It has also been proposed to provide the electrodes which form the micrometer spark gap as a pair of surfaces, one of which is usually stationary and the other of which approaches it laterally so that the surface of the moving electrode passes at a predetermined distance past the fixed electrode. This is sometimes accomplished by providing the moving electrode as a segmental conducting surface in the circumference of a rotary member and providing the fixed electrode as a species of brush which clears the rotary member by the required distance. This arrangement is, however, unsatisfactory because the initial sparking when the two surfaces approach one another invariably occurs along the approaching edges of the surfaces and persists until sparking occurs between the opposite edges of the electrodes just prior to their separation from one another far enough to eliminate sparking altogether. Although this method is relatively effective in keeping the micrometer spark gap free of ionized air and foreign material, the apparatus is relatively costly to construct because of the extremeprecision of the gap which must be formed at each revolution of the rotary member over long periods of time and, more particularly, because of the variableness of the utilizable areas of the elec trodes at the beginning, during the main part of and at the end of the sparking period. While it is characteristic of the sparking of a high frequency current across a well ventilated and cooled gap between perfectly plane and parallel surfaces that little or no pitting of the electrode surfaces or metal transfer occurs because of the intermittent and extremely rapid oscillation of the spark, this condition does not prevail over the entire sparking period when one of the electrodes rotates or moves past the other in the manner just mentioned. Asa result, extensive pitting along the leading and trailing edges of the two electrodes occurs, with the net result that after operating for a short while the gap is no longer stabilized.

None of the proposals made heretofore for stabilizing a micrometer spark gap, such as that comprising an essential part of the circuit with which the present invention is concerned, provides for a complete stabilization of the gap between each sparking across the gap. It is apparent that for complete stabilization not only should the space between the electrodes be purged of all foreign solid material and all ionized air but that the electrodes, if moved during the cleaning operation, should be returned to their precise locations with respect to one another both as regards the distance between them and, equally importantly, as regards the parallelism of the electrode surfaces and the lack of displacement of one surface laterally with respect to the other.

According to the present invention, the stabilization of the micrometer spark gap in the primary high frequency circuit of a high frequency, high tension ignition system is effected between each sparking of the gap by moving one, or both, of the electrodes so that one of them is displaced rapidly with respect to the other in a direction substantially normal to the faces of the electrodes and then, before the time at which the next sparking is to occur, returning it to its original exact position. In this manner there is created between the electrodes a highly turbulent, high velocity movement of air in a direction parallel to the electrode surfaces Which not only effectively cleans the space between them of all solid foreign matter, but also blows essentially all of the ionized air from between them. The gap is thus cleaned and reformed after each sparking with a degree of uniformity such that subsequent sparkings occur under precisely the same conditions as the first and at precisely the same critical value of the charge on the condenser.

It is to be understood, of course, that the movement of the electrode, or electrodes, can be such that the distance between them is either increased or decreased to effect the desired result. In certain instances, as when a make and break means is required to be in the circuit to form and interrupt a shorted magneto circuit to facilitate starting or operation at very slow engine speeds, it is advantageous to effect the purging of the gap by causing the distance between the electrodes to decrease and to actually cause the electrodes to contact one another to function as the make and break means. In such an instance provision is made, as will be explained later, to reform the gap so rapidly following the break that it becomes stabilized well before the charge on the condenser has built up to the critical value. In other instances it may be more advantageous to provide a separate make and break means, if one is desired, and to increase rather than decrease the distance between the electrodes to effect purging since it is generally possible to alter the distance between the electrodes to a greater extent in this manner and to thus effect a more vigorous purging action. Alternatively, and preferably in some instances, the means for varying the length of the micrometer spark gap can also be adapted, as will be described, to effect the forming and interrupting of the shorted magneto circuit, but not utilizing the micrometer spark gap electrodes as the circuit forming and interrupting means. Provision can also be made for automatic shifting of such make and break timing to fully automatic waveform timing, and vice versa, according to the engine speed.

It is, of course, understood that the actual distance between the electrodes in the stabilized micrometer spark gap, which can preferably be adjusted by suitable means, will, for best performance, depend to a considerable extent upon the characteristics of the other elements in the circuit. The gap should not be so short that sparking will occur before the charge on the condenser has reached the desired critical value. On the other hand, if the gap is so long that it requires too high a critical value of the condenser charge, unsatisfactory results may be obtained at low engine speeds and during starting. The distance between the elec trodes, i.e. the length of the micrometer spark gap when the electrodes are adjusted properly and the gap stabilized, is herein, for convenience sometimes referred to as the predetermined distance between the electrodes or the predetermined length of the gap.

The invention can be understood readily from the accompanying drawing showing representative circuits and mechanical means useful in practicing the invention, wherein, in the interest of clarity, certain of the mechanical features are shown on a somewhat exaggerated scale and wherein Figure 1 is an illustration of the symbol sometimes used herein to represent a micrometer spark gap, the length of which is caused to vary in a cyclic manner from a predetermined length;

Figure 2 is a diagram of a representative circuit employing a micrometer spark gap, a high frequency transformer and a condenser suitable for practicing the invention employing wave-form timing of an engine running at high speed;

Figure 3 is a diagram of a variation of the circuit of Figure 2 sometimes employed;

Figure 4 is a diagram of another variation of the circuit of Figure 2 sometimes employed;

Figure 5 is a diagram of a circuit similar. tothat of Figure 2 but illustrating schematically how to separate make and break means can be included in the circuit to facilitate starting of the engine and its running at low speeds;

Figure 6 is a diagram of a circuit similar to that of Figure 5, but differing therefrom in that the micrometer spark gap also serves as the make and break means, and illustrating schematically one way in which magnetic means can be employed to operate the micrometer spark gap;

Figure 7 is a diagram of a circuit similar to that of Figure 5 but illustrating schematically one way in which rnechanical means can be employed to operate the micrometer spark gap;

Figure 8 is a diagram of a circuit similar to that of Figure 5 but illustrating schematically another way in which mechanical means can be employed to operate the micrometer spark gap;

Figure 9 is a diagram of a circuit similar to that of Figure 6 and showing yet another way in which mechanical means can be employed to operate the micrometer spark gap;

Figure 10 is a diagram of a circuit of the invention but showing still another way in which mechanical means can be employed to operate the micrometer spark p;

Figure 11 is a diagram of a circuit of the invention but showing still another way in which mechanical means can be employed to operate the micrometer spark gap.

Figure 12 is a digram of a circuit of the invention but showing still another way in which mechanical means can be employed to operate the micrometer spark p;

Figure 13 is a diagrammatic sketch showing an armature plate of an outboard engine in plan and a flywheel in section and illustrating one way in which the ignition system of the invention can be utilized with such an engine;

Figure 14 is a schematic sectional elevation of a variation of the arrangement of Figure 13;

Figure 15 is an enlargement of a variation of a portion of the apparatus of Figure 13;

Figure 16 is a partial plan and sectional view corresponding to Figure 13, but showing a different arrangement of certain of the parts; t

Figure 17 is an elevation, principally in section, taken along the line XVII-XVII of Figure 16; and

Figure 18 is a bottom elevation, principally in section, taken along the line XVIII-XVIII of Figure 17.

The symbol of Figure 1 when employed herein is utilized to represent a stabilized micrometer spark gap comprising an essential part of the circuit of the inven tion. As indicated previously, the micrometer spark gap, as represented by the symbol of Figure 1, is formed with two electrodes having parallel facing surfaces at a predetermined distance from one another although provision is made according to the invention, as will be explained later, for varying the length of the micrometer spark gap in an intermittent or cyclic manner from the predetermined length. The length of the gap in any particular arrangement or circuit is invariably the predetermined length and the gap is invariably stabilized immediately :prior to and during the interval of the cycle when spark- ;ing across the gap begins. 1

The circuit of Figure 2 comprises a micrometer spark gap 21, the primary coil 22 of a high frequency transformer and a suitable condenser 23 connected in series in a primary high frequency circuit, the balance of the ...circuit in this instance being through ground. The secondary coil 24 of the high frequency transformer is ...connected in series in a secondary high frequency circuit -with the condenser 23', a conventional distributor 25, when required, and a conventional ignition spark gap,

such as a spark plug 26, the balance of this circuit also being' through ground. Current is supplied for the operation of the primary high frequency circuit from the coil 27 of a magneto wound to produce a current having voltage wave-form characteristics suitable for automatic wave-form timing. The magneto coil 27 is connected in a magneto circuit in series with the primary coil 22 of the transformer and the condenser 23, the balance of this circuit being through ground. In the modification of Figure 2 the micrometer spark gap 21 is connected across the magneto and is thus in parallel in the magneto circuit with the primary coil 22 and the condenser 23, but is in series with the primary coil 22 and the condenser 23 in the primary high frequency circuit, as required by the invention. In operation of the system, the magneto charges the condenser 23 during each voltage cycle with a current of increasing voltage. When the charge on the condenser 23 reaches a critical value such that it is able to overcome the resistance of the micrometer spark gap 21, discharge of the condenser 23 across the gap 21 occurs thus setting up a high frequency oscillating current in the high frequency circuit through the primary coil 22.

Sparking will continue across the micrometer spark gap 21. during the entire part of the voltage cycle of the magneto current in which the charge on the condenser is maintained as great as the critical charge and will persist for an appreciable interval of time thereafter until the voltage of the magneto current has dropped somewhat below that necessary to maintain the critical charge on the condenser. This is due to the instability and drop in resistance of the micrometer spark gap 21 resulting from the presence within the gap of ionized air caused by the initial and subsequent sparking. When the voltage of the magneto current becomes so low that the condenser 23 is no longer able to maintain the spark across the micrometer spark gap 21, even in its unstabilized condition, the flow of high frequency current through the primary coil 22 of the high frequency transformer will cease. The operation will be repeated, subject to the limitations given previously, during the next period of increasing voltage of the output of the magneto coil 27 even though the next wave be opposite in polarity from the first.

During the time the high frequency oscillating current is flowing through the primary coil 22, a high frequency, high tension current is generated in the secondary coil 24 of the transformer sufficient to cause sparking at the ignition spark gap 26. Sparking at the ignition spark gap 26 Will continue as long as sparking continues across the micrometer spark gap 21. It is, of course, understood that the ignition spark gap 26 may be one of a group, as in a multi-cylinder engine, and that the particular member of the group which fires is dependent upon the distribution effected by the distributor 25. It is, of course, further understood that the wave form of the magneto current is synchronized with the travel of the piston in the particular cylinder which is to be fired. Generally, this synchronization is arranged so that the maximum voltage of the current output of the magneto coil 27 is attained at practically the same time that the piston is at the top of its compression stroke. It will also be apparent that in multi-cylinder engines a new wave of increasing voltage must be generated each time any one of the combustion charges is to be fired and that synchronization must be effected accordingly. Under such conditions, employing a magneto coil wound to give a current with a voltage wave form of suitable configuration which is repeated at suitable intervals, automatic wave-form timing and firing of the combustion mixture in the combustion chambers of the engine in desired sequence is obtained so long as the engine is running at a speed suflicient to yield a current output from the magneto coil 27 which attains a voltage high enough to charge the condenser 23 to the critical value and, most importantly, so long as restabilization of the micrometer spark gap 21 is effected after each discharge across it and before the next. Automatic advancement of the spark at the ignition spark gap 26 results in known manner when the magneto coil is wound to give a properly shaped voltage wave form.

In .some instances it may be desirable to connect a second condenser 31, of larger capacity than the condenser 23, across the magneto coil 27 in parallel with the micrometer spark gap 21, as illustrated in Figure 3, to improve the sparking characteristics of the gap 21. Under such conditions both of the condensers 23 and 31 will become charged to the critical value at the same time. This has the added effect of increasing the flow of high frequency oscillating current through the primary coil 22. In still another alternate form of the circuit, illustrated in Figure 4, the micrometer spark gap 21, the condenser 23 and the primary coil 22 can be connected in series in both the magneto circuit and the high frequency primary circuit.

The circuits of Figures 2, 3 and 4 are well adapted to use as the ignition system of an internal combustion en gine once the engine has been started and is running at moderate to high speeds, provided the micrometer spark gap 21 has the requisite stability characteristics. It is generally advisable to provide, in connection with the circuits illustrated in Figures 2, 3 and 4, a make and break means in the magneto circuit for use during periods of starting or of low engine speeds to insure adequate functioning of the ignition system when the magneto may not be furnishing current at a voltage sufiiciently high during any part of the cycle to charge the condenser 23 to the critical value. In one such arrangement, illustrated schematically in Figure 5, a make and break device 32, often referred to as a circuit-forming and interrupting means, is connected across the magneto circuit in parallel in the circuit with the magneto coil 2'7. The magneto coil 27 and the circuit forming and interrupting means are thus connected in series in a shorted magneto circuit. In operation, the shorted magneto circuit is maintained until such time as sparking is required at the ignition spark gap 26. At the proper time in the cycle the shorted magneto circuit is interrupted by the circuit making and interrupting means 32 When this occurs, a self induced surge current of high voltage adequate to charge the condenser 23 to the critical value is setup in the magneto coil and the charged condenser then discharges across the micrometer spark gap 21 as described previously. In this way adequate sparking at the ignition spark gap 26 is obtained at very low engine speeds and no difliculty is encountered in starting the engine even under very adverse conditions. A switch 33 can be provided in series with the make and break means 32 whereby the latter can be disconnected, either manually or automatically in response to the engine speed, and rendered inoperative after the engine has started and full wave-form timing then utilized.

As explained previously, and as emphasized here, it is essential that the micrometer spark gap 21 not only be of precisely the same predetermined length at each time the condenser 23 becomes charged at the critical value but that, during the part of the voltage cycle when this condition of the condenser '23 does not prevail, the gap 21 be cleaned and ventilated to purge it of all accumulated dirt and ionized air, by varying the distance between the electrodes rapidly in a direction normal to their surfaces, and then restored to its precise predetermined length for an appreciable time prior to the attainment of the critical charge on the condenser to allow it to become perfectly stabilized so that there is not the least vibration in the mechanical parts which would cause an oscillation in the length of the gap and so that the circulation of air within the confines of the gap has substantially ceased. In addition, the precise parallelism of the electrode surfaces in the stabilized gap must be maintained and care must be taken to avoid lateral displacement of one electrode surface with. respect to the other to avoid localized sparkingwhich would lead to pitting and burning of the surfaces and a. rapid loss in accuracyof timing. In view of the extreme shortness of the gap as generally employed and the extreme rapidity of firing in a fast-running engine, the difliculty of fulfilling all the requisite conditions ,using apparatus and methods hereto! fore devised is apparent. Only by moving one or both. of the electrodesforming the micrometer spark gap 241 in a direction normal to their surfaces as herein first described so that the space between them either increases or decreases from the predetermined distance has it been found possible to effect the desired result and to provide invariably a stabilized gap for each discharge of the condenser 23. Certain illustrative magnetic and mechanical means for accomplishing these effects with a high degree of accuracy and at high speed will be described in con nection with the ensuing figures.

It should be pointed out that in Figures 6 to 12, in: elusive, the arrangement and function of the primary and secondary coils 22 and 24 of the high frequency transformer, the condenser 23, the distributor 25, if employed, and the ignition spark gap 26 are identical with the arrangement of the same elements in Figures 2, 3 and 5 and that the description of these elements and their operations in connection with Figures 6 to 12 would be merely repetitious and will be avoided. It is also fur ther pointed out that the alternate arrangement of the micrometer spark gap 21, primary coil 22 and condenser 23 shown in Figure 4 can, in general, be utilized equally well in arrangements of Figures 6 to 12, inclusive, and such arrangements are contemplated by the invention. Furthermore, it is understood that a condenser corresponding to the condenser 31 of Figures 3 and 4 can also be employed if desired.

As mentioned previously, the micrometer spark gap in the ignition system of the present invention can, if desired, be arranged to serve as the shorted magneto circuit forming and interrupting means in addition to its normal function while at the same time the necessary purging of the gap between intervals of its functioning at its predetermined length is effected. One way in which this can be accomplished magnetically is illustrated schematically in Figure 6 wherein one electrode 34 of the micrometer spark gap 21 is mounted in a fixed position and the other electrode 35 is mounted at one end of a suitable springleaf 36. The other end of the spring leaf is secured in a fixed insulated position as illustrated at 37. An insulated adjusting screw 38, also mounted in a fixed position, is provided by means of which the distance separating the electrodes 34 and 35 can be adjusted to a predetermined value, it being understood that the mounting of the spring member 36 is such that it is tensioned against the end of the adjusting screw 38.

A suitable rotary member 39 is mounted and rotated, by conventional means not shown, in synchronization with the engine piston. The rotary member 39 is mounted in a position such that its circumference is closed adjacent the spring member 36 on the same side thereof as the fixed electrode '34. A suitable magnet 43 is mounted in the rotary member with its surface flush with the circumferenoe of the member. As the member 39 rotates, the magnet 43 thus alternately approaches and recedes from the spring member 36. A shoe 44 of iron or other magnetically susceptible material is secured to the spring member 36 so as to be attracted strongly by the magnet 43'at intermittent periods as the member 39 rotates and the magnet is in its vicinity. During the periods of attraction of the shoe 44 by the magnet 43 the movable electrode 35 is caused to approach and contact the fixed electrode 34, thus forming .a shorted magneto circuit through the two electrodes. As the member 39 rotates further, the-magnet 43 recedes from the shoe 44 and the tension of the spring member 36 overcomes themagnetic attraction, with the result that the electrode 35 separates from the fixed electrode 34 and is returned rapidly by the tension of the spring member 36 to its original position, thus restoring the micrometer spark gap 21 to its predetermined length. An insulated supplementary spring 42, preferably adjustable as to tension, can be provided, if desirable or necessary, to provide for finer adjustment of the tension effecting the return of the micrometer spark gap to its predetermined length. During this operation of closing and opening, the gap becomes thoroughly cleaned of any solid particles and of ionized air due to the violent expulsion of air from between the electrodes during the closing motion and to the violent rush of fresh air into the gap during the separation of the electrodes.

Since it requires an appreciable time for the condenser 23 to become charged to the critical value following the actual interruption of the shorted magneto circuit at the instant of separation of the electrodes 34 and 35, adequate time is provided for the gap to be reestablished at its predetermined length, for all vibration of the spring member 36 to cease, for the air within the gap between the electrodes to become quiet, and for the gap thus to become thoroughly stabilized prior to the accumulation of the critical charge on the condenser 23. It is, of course, apparent that vibration of the spring member 36 is minimized by locating the gap-adjusting screw 38 in the immediate vicinity of the movable electrode 35. It is also apparent that the arrangement described provides for a very quick and accurate reforming and stabilizing of the gap following the actual separation of the two electrodes.

The arrangement just described provides sparking at the ignition spark gap 26 at a very low engine speed, e.g. during starting, and also provides for automatic conversion to complete the waive-form timing as soon as the speed of the engine reaches a certain value, dependent largely upon the tension on the supplementary spring 42. When the tension on this spring is adjusted properly and the magnetic coaction of the magnet 43 and the shoe 44 are in suitable relationship, the attraction of the magnet 43 on the shoe 44 is of such character and of such short duration that the combined inertia of the shoe 44, the leaf spring 36 and the supplementary spring 42 is not overcome sufficiently to cause the electrodes 34 and 35 to actually contact one another at high engine speeds. Complete wave-form timing thus results. However, the attraction of the magnet 43 for the shoe 44 is suificient even at high engine speeds to cause the spring member 36 and the movable electrode 35 to vibrate or flutter to such an extent that adequate ventilation and cleaning of the gap 21 is effected. In other words, at high engine speeds the electrode 35 approaches, but does not contact, the fixed electrode 34. The constant forcing of air out of the gap and the drawing of new air into the gap by this motion of the electrode 35 effectively cleans the gap even though the electrodes do not actually contact one another. At low engine speeds the arrangement, of course, reverts to mechanical timing, the change from one form of timing to the other being fully automatic in all cases.

The attraction of the magnet 43 for the shoe 44 is of further advantage even when the timing is entirely wave form in character. At higher engine speeds, the time of the critical voltage value of the wave advances sufficiently to cause discharge of the condenser 23 across the micrometer spark gap 21 well before the magnet approaches the shoe closely enough to decrease the length of the gap. As the voltage falls on the other side of the wave, the attraction of the magnet for the shoe becomes effective and decreases the length of the gap, even though the electrodes do not come into contact, at the time when the discharge of the condenser across the gap would otherwise cease, with the very desirable result that the time of the discharge, and hence of the sparking at the ignition gap, is prolonged thus leading to improved ignition.

It is to be noted that the shoe 44 at no time canteen the magnet 43 or any other part of the circumference of the rotary member 39 and for this reason there is no wear whatsoever on either the magnet 43 or the shoe 44, The arrangement shown is thus capable of operating con= tinuously over long periods of time Without appreciable change in its operating characteristics.

The modification of Figure 7 illustrates one way in which a mechanical means can be employed both to vary the length of the micrometer spark gap from its prede termined length to efiect purging and ventilation of the gap and to make and interrupt a shorted magneto circuit. In this modification, one of the electrodes 45 of the micrometer spark gap 21 is mounted at one end of? an elongated flexible conducting member 46, the other end of the member 46 being secured rigidly in an insulat-- ing block 47. The other electrode 48 of the gap 21 is mounted on an elongated spring leaf facing the electrode 45, one end of the leaf 49 also being secured rigidly in the insulating block 47. The unsecured end of the leaf 49 projects for a suitable distance beyond the electrode 48. A rotary cam 52 of conducting material is provided having a cam riser 53 extending for a desirable distance around the circumference of the cam 52. The cam 52 is rotatably mounted in a position such that as it rotates the riser 53 contacts the projecting end of the leaf 49 on the side thereof on which the electrode 48 is mounted and lifts it, but so that the main body of the cam 52, exclusive of the riser 53, does not contact the leaf 49. Due to this action the electrode 48 is moved away from the electrode 45 each time the cam 52 revolves. When the riser 53 disengages the end of the leaf 49, the latter, because of its springiness, returns the electrode 48 to its original position. In this manner the gap 21 is purged and reformed in a stabilized condition for each revolution of the cam 52.

The predetermined length of the gap 21 is controlled by a suitable adjusting screw 38 which threadably engages the conducting member 46 and prevents the length of the gap 21 becoming less than the predetermined length. It is to be noted that the adjusting screw 38 is insulated at its tip 30 from the leaf 4 9 in suitable fashion. The trailing edge 54 of the cam riser 53 is preferably undereut to facilitate sharp separation of the riser and the leaf 49 and to enable the leaf 4-9 to return to its position of contact with the adjusting screw 38 with great rapidity as soon as its projecting end drops off the riser 53.

In practice, one terminal of a magneto coil 27 is connected to the leaf 49 and to the primary coil 22 of the; transformer and the other terminal is connected, gen-- erally through ground, to the electrode support 46 and' to the rotary cam 52, including the riser 53. A switch 55 is provided whereby the shorted magneto circuit:

through the leaf 49 and the cam 52 can be broken as; desired. When so connected and the rotary member 52: rotated in the direction shown, the riser 53 and the leaf? 49 constitute a shorted magneto circuit making and in-- terrupting means as well as a mechanical means for purging and ventilating the micrometer spark gap 21. When the leaf 49 is in contact with the cam riser 53, with the switch 55 closed, the shorted magneto circuit is completed through the cam. When, however, the projecting end of the leaf 49 drops off the riser 53, the shorted magneto circuit is interrupted and a surge of high voltage current is induced in the magneto coil 27 sufiicient to charge the condenser 23 to its critical value, whereupon the condenser discharges across the stabilized gap 21, thus setting up a high frequency current in the primary coil 22 of the transformer and firing the ignition gap 26 in the manner heretofore described. It is to be noted that, because of the time required following the separation of the electrodes 45 and 48 for the charge on the condenser to build up to its critical value, there is. ample time for the gap 21 to be reformed and to becomestabilized at its predetermined length before. the condenser acquires its critical charge. It is noted also, that themicrometer spark gap 21, the primary coil 22 of the high; frequency transformer and the condenser 23 are connected, in series in the high frequency primary circuit.v

To convert the arrangement shownin Figure 7 to automaticywave-form.timing, the switch 55 can be opened, either manuallyv or: automatically in response to the engine; speed. Whenthe switch 55 is opened, current no longer flows between the, leaf 4% and the cam riser 53 whenthey are in-contact and fully automatic wave-form timing is effected, the cam still effecting purging and ventilation of the micrometer spark gap 21. as before.

Alternatively, the change, to wave-form timing can be provided for by arranging the parts so that the adjusting screw, 38 rests on a spring-tensioned ram 56 rather thanbeing mounted in a fixed member 57 of the apparatus. The ram 56 itself is held firmly, as by a spring 58, in a fixed, but adjustable, position with respect to a fixed member 57 of the apparatus. When the ram 56 is adjusted with respect to the fixed member 57 so that the.

cam riser 53 contacts the leaf 4%, make and break timing will occur as described. When, however, theposition of the-ram 56 is adjusted, asby turning it 90 degrees so that the pin 50 lies in the slot 51 in the fixed member 57 whereby contact between the leaf 49 and the riser53 no longer occurs, wave-form timing will result. The same result can be accomplished by mounting the insulating block 47 and the adjusting screw 38 on a common rigid member of the apparatus which can be rotated slightly to prevent contacting of the leaf 49 with the cam riser 53. In the latter instance the provision of the ram 56 is unnecessary. Both of these latter methods for con: verting the apparatus of Figure 7 to wave-form timing have the disadvantage that during wave-form timing no provision is made for purging and ventilating the rnicrometer spark gap. For this reason conversion to waveform timing is preferably accomplished employing the switch 55, or its equivalent.

In still another modification illustrated in Figure 8, which is somewhat similar to the modification of Figure 7, a rotary cam 52 having a cam riser 53 is provided asbefore, the cam :72 being grounded. In this instance, however, three leaf springs 46, 62 and 59 are provided, the electrode 48 being mounted on the center leaf 62. The other electrode 45 of the micrometer spark gap 21 is mounted near one end of the lower leaf 46. One end of each of the three leaves 46, 59 and 62 is secured rigidly in an insulating block 47. An adjusting screw 38, mounted in a fixed member 63 of the apparatus engages the lower leaf !6 threadably and furnishes a means for adjusting the micrometer spark gap 21 at its predetermined length, the central leaf 62 being tensioned to lie normally in contact with the end-of the adjusting screw 38. The upper spring member 59, which projects past the free end of the leaf 62, forms a make and break con: tact with the cam riser 53 in the same way as the leaf 49 of Figure 7.

The leaf 59, the leaf 62 and the ungrounded terminal of the high frequency coil 22 are each connected to one terminal of the magneto coil 2-7 and the leaf 46 and the rotary cam 52 are each connected to the opposite terminal of the magneto coil, usually through ground. A switch 64 is'provided whereby the shorted magneto circuit through the leaf W and the rotary cam 52 can be broken when desired. The leaf 59 is also providedwith an insulated .lift hook 65 which, as the leaf 59 is raised by the cam riser 53, engages the leaf 62 and increases the distance separating the electrodes 48 and 45. When the cam 53 disengages the leaf 59, the electrode 48 immediately returns to its original predetermined position determined by the setting of the adjusting screw 38. By this sequence of operations the micrometer spark gap 21 1s purged and ventilated and reformed in a stabilized condition at its predetermined length, the generation of a} spark in the ignitionspark gap 26 occurring in a manner identical with that explained previously in connection with Figure 7.

Conversion to automatic wave-form timing is effected switch 64 can either be by manual means or by means responsive to the speed of theengine. However, the leaf Sit and the cam 53 continue to function as a mechanical means for purging the micrometer spark gap 21.

In the modification shown in Figure 9, intended'primarily for mechanical timing, a grounded rotary cam 52- having a cam riser 53 similar to that of Figure 7 is also utilized. In this modification, however, an elongated leaf spring 66 is provided, one end of which is secured in an insulated mounting 47' and the other free end of which-is adapted to engage the cam riser 53. instance one of the electrodes 48 ofthe micrometer spark gap 21 is secured to the leaf 66 at a convenient point removed from its free end and on the side of the leaf opposite that engaged by the cam riser 53. The other electrode 45 of the gap 21 is mounted near the free end of a second leaf spring 67, the opposite end of which is also secured in the insulating support 47. The electrodes 45 and 48 face one another and have substantially parallel facing surfaces.

An adjusting screw 38 threadably engaging a fixed support 68, which is preferably grounded, engages the side of the leaf 66 opposite the electrode 43 under tension of the leaf 66 and serves to regulate the length of the micrometer spark gap 21 by limiting the travelof the leaf 66 after it is disengaged by the undercut end'54 of the cam riser 53. The leaf 67 carrying the electrode. 45 presses against a suitable arresting member 69 which restrains the spring action of the leaf 67 and prevents the electrode 45 from moving past a predetermined position toward the electrode 48. In the illustration shown, the leaf 69 is clamped in the insulating mounting along with the leaf 67, although any other provision for restraining the movement of the electrode 45 in similar manner can be employed.

One terminal of the magneto coil terminal 27 is connected to the leaf 67 and to the ungrounded terminal of the high frequency primary coil 22 and the other magneto coil terminal is connected, usually through ground, to the rotary cam 52 and the leaf 66.

In operation, with the micrometer spark gap 2-1 adjusted carefully at its predetermined length by means of the adjusting screw 38, the revolution of the rotary cam- 52 causes the electrode 48 to approach and contact the electrode 45. The precise height of the cam riser 53. and, therefore, the distance through which the electrode 48 travels is not critical because the electrode 45 is free to be moved out of its position of rest because of the spring character of the leaf 67. the leaf' 66 is disengaged by the riser 53, the leaf 67 springs back to its original position in contact with the arresting member 69 and the leaf 66 springs hack to itsposition of rest on the adjusting screw 38. This sequence of operations thus serves as a make and break, by the contacting and separation of the electrodes 4-5 and- 48, for the shorted magneto circuit through the leaf 67, the electrodes 45 and 48, the leaf 66 and thence directly to ground or through the cam 52 to ground. At the same time, the micrometer spark gap 21 is adequately purged, ventilated and reformed at its original predetermined length and in its original stabilized condition after each discharge of the condenser 23 across it.

According to the modification of Figure, 10, a cam is also provided, suitably a-, circular member 78 with. a.

In this instance three leaf springs 73, 74-v In' this- When the free end of' ga ses and 75 are provided, one end of each being secured in an insulating block 47 and the leaf 74 being mounted between the leaves 73 and 75. Although it will be understood that the positioning of the leaves 73, 74 and 75 is unimportant except with respect to their coaction with one another, they will here sometimes be referred to, for the sake of convenience, as the upper, intermediate and lower leaves, respectively, the same being true in the description of certain parts of the other figures of the drawing. Each of the three leaves is provided at a suitable distance from the insulated mounting 47 with an electrode or contact point, the electrode on the inter mediate leaf 74 lying between and facing the other two. The electrode 45 on the upper leaf 73 is on the lower side of the leaf and the electrode 76 on the lower leaf 75 is on the upper surface of the leaf. The electrode 48 on the intermediate leaf 74 extends through the leaf and, in cooperation with the electrode 45, constitutes a micrometer spark gap and, in cooperation with the contact point 76, constitutes a make and break means, as will be apparent. The upper leaf 73 is connected to one terminal of a magneto coil 27, to the ungrounded terminal of the primary coil 22 of a high frequency transformer and, through a suitable switch 77, to the lower leaf 75. The intermediate leaf 74 is connected to the opposite terminal of the magneto coil 27, usually through ground. The cam 78 in this instance forms no part of the circuit although it can be grounded, if desired.

An adjusting screw 38 for adjusting the micrometer spark gap 21 to its predetermined length is threadably secured to the upper leaf 73 so that it travels with the leaf with its lower end in contact with the intermediate leaf 74 when the gap 21 is at its predetermined length. The adjusting screw 38 is insulated either from the upper leaf 73 or from the intermediate leaf 74, or from both, so as to prevent the passage of current from one leaf to the other through the screw. A rigid arresting member 79 is also provided to limit the upward travel, but not the downward travel, of the lower leaf 75, and a second arresting member 70 is provided to limit the downward travel of the upper leaf 73 but not its upward travel. The three leaves 73, 74 and 75 are tensioned in the mounting 47 in such a manner that the upper and intermediate leaves '73 and 74 are continually urged downward whereas the lower leaf 75 is continually urged upward. The leaf 74 thus follows the surface of the cam 78, the leaf 75 rests against the arresting member 79 except when dislodged therefrom by the downward movement of the leaf 74 and the leaf '73 rests continually against the arresting member 78 except when lifted therefrom by the intermediate leaf pressing on the adjusting screw 38. In the modification shown, the arresting members 79 and 78 are rigid leaves secured in the insulating support 47 along with the lower leaf 75 and the upper leaf 73, respectively, but any other convenient arresting means can be employed.

The free end of the intermediate leaf 74 is prolonged beyond the electrode 48 and the rotary cam 78 is located so that the intermediate leaf '74 is urged upward into contact with the adjusting screw and lifts the leaf 73 during that part of the rotation of the cam 78 when the end of the leaf 74 is on the high part of the cam. By this operation the micrometer spark gap 21 is maintained at its predetermined length during this interval. After the end of the leaf 74 is disengaged from the high part of the cam 78, the tension on the leaf 74 forces the electrode 48 downward into contact with the contact point 76, thus forming a shorted magneto circuit. At the same time, the electrode 45 fails to follow the electrode 48 downward through its entire travel because of the arresting of the leaf 73 by the arresting member 78, with the result that the length of the micrometer spark gap 21 is increased, thus effecting cleaning and ventilation of the gap. As the cam 78 rotates further, the intermediate leaf 74 is again lifted breaking the contact between the '14 contact point 76 and the electrode 48. The charging of the condenser 23 begins and the micrometer spark gap 21 is reformed and stabilized at its predetermined length as soon as the leaf 74 contacts the adjusting screw 38. Further lifting of the leaf 74 by the cam merely lifts the upper leaf 73 as well without altering the length of the micrometer spark gap 21.

It is also apparent that by suitable adjustment of the parts the gap 21 can be reformed either before the contact points 48 and 76 become disengaged or as soon thereafter as is necessary for the gap to become stabilized for a brief interval before the condenser 23 has become charged to its critical value. The entire sequence thus provides mechanical make and break timing, utilizing the electrodes 48 and 76, as well as mechanical means for purging and ventilating the micrometer spark gap 21, in this instance by separating the electrodes 45 and 48 to a distance greater than the predetermined length of the gap. The arrangement can be converted either manually or automatically to wave-form timing at higher engine speeds by opening the switch 77. Current then no longer flows in the leaf 75 and the electrode 76, but the apparatus continues to function as a mechanical means for cleaning and reforming the micrometer spark gap 21 after each discharge of the condenser 23.

In the modification shown in Figure 11, a pair of leaf springs 82 and 83 are provided with one end of each secured rigidly in an insulating mounting 47. A pair of electrodes 45 and 48, which form a micrometer spark gap 21, are mounted facing each other near the free ends of the leaves 82 and 83. One of the leaves 82 is equipped with an adjusting screw 38 which engages the leaf 82 threadably and which is insulated from the leaf 83. By adjusting the screw 38, the micrometer spark gap 21 can be set at its predetermined length. The free end of the leaf 83 engages a cam riser 84 on the surface of a rotary cam 85. The cam riser 84 has an undercut trailing edge 86 to facilitate rapid disengagement of the end of the leaf 83 from the riser 84. In this instance the riser 84 and the rotary member are constructed of an insulating material except for a segment 87 of conducting material which includes the trailing edge of the cam riser 84, a short adjacent portion of the surface of the riser 84 and a short adjacent portion of the surface of the cam body 85. The conducting segment 87 also has an undercut trailing edge 81. The mounting and tensioning of the leaf 83 is adjusted so that its free end follows the cam riser 84, including the fore part of the surface of the segment 87, and, after disengagement therefrom, drops to and follows the lower surface 88 of the segment 87 from which it then drops to and follows the insulating surface of the rotary cam body 85 until it is again engaged and lifted by the cam riser.

The leaf spring 82 is mounted and tensioned so that the end of the adjusting screw 38 engages the leaf 83 when the free end of the latter is following the cam riser 84 but so that it is disengaged from the leaf 83 when the free end of the latter is following the surface of the cam body 85. An arresting member 80, similar to the arresting member 70 of Figure 10, is advantageously employed to arrest the movement of the leaf 82 downward and insure lengthening of the gap 21 from its predetermined length when the cam riser 84 disengages the leaf 83. The micrometer spark gap 21 is thus longer than its. predetermined length during that portion of the rotation of the member 85 when the free end of the leaf 83 is disengaged from the cam riser 84, but is at its predetermined length when the free end of the leaf 83 is following the cam riser 84.

The free end of the leaf 82 carrying the electrode 45 is forced upward by the pressure of the leaf 83 on the adjusting screw 38 without changing the length of the micrometer spark gap from its predetermined length if this is necessary to enable the free end of the leaf 83 to follow the cam riser easily. The micrometer spark gap 21 15 is thusalternately lengthened from and shortened again to its predetermined length whereby its cleaning and resta-bilization are effected accurately.

The leaf 83 and the ungrounded terminal of the primary coil 22 of the high frequency transformer are connected to one terminal of a magneto coil 27 and the leaf 82 and the conducting segment 87 of the rotary cam 85 are connected to the other terminal of the coil 27, usually through ground.

In operation, this modification provides completely automatic wave-form timing of an engine running at moderate and high speeds as well as automatic shifting to'mechanical timing when thespeed of the engine is low enough torequire it; With proper synchronization of the rotary cam 85 with the piston of the engine, eg with the cam riser synchronized to disengage the leaf 83 when the piston is at approximately the top of its compression stroke, the magneto charges the condenser 23 to its critical value causing" its discharge across the micrometer spark gap 21 while the end of the leaf 83 is following the cam riser 84. Because of the broadening of the wave form at the critical voltage at moderate andhigh engine speeds, and the consequentadvance in timing, sparking across the gap 21- and firing in the cylinder will, under all normal conditions of operation of the engine, occur well before the end of the leaf 83 contacts the conducting segment 87 and the formation and interruption of the shorted magneto circuit will be without effect on the runing of theengine; In other words, the timing willbe completely dependant upon the wave form of the magneto current voltage. When, however, the engine speed is solow, as in starting, that the voltage of the magneto current is insufficient to charge the condenser 23 to its criticalvalue, no discharge will occur across the micrometer spark gap 21 until'the leaf 83 contacts the conducting segment 87. This will form a shorted'magneto circuit through the leaf' 83'and the.conducting segment 87 and cause a surge of high voltage current in the magneto coil 27; This in turn will charge the condenser to its criticalv-alue causingjit to discharge across the microm-- eter spark gap 21. The high frequency oscillating current thus set up in the primary coil 22 of the high frequency transformer induces the desired high frequency high tension currentiin the secondary coil 24 of' when the trailing edge of the cam riser 84 disengages.

the leaf 83; formed again .When the leaf 83 falls onto the lower surface 88 ofthe segment 87 and again interruptedwhen the leaf 83'drops from the trailing edge of the surface 88- of the segment 87. Each time the shorted magneto'circuit is formed or interrupted'there is a rapid change of flux in the magneto field. In instances of extr'emely low engine speeds it'is possible that the charge on-the condenser will not reach the critical value causing it-to' discharge across'the micrometer spark gap 21 at either the'fi'rst formation or the first interruption of the shorted magneto circuit. In most such instances the approach ofthe end of theleaf 83, after it is disengaged by the cam-riser 84, to the lower surface 88'of the segment87'f0-rrns a gap ofrlecreasing length across which the condenser23, even though its charge be less than the critical charge, will discharge before contact is made, the leaf83 and the surface 88 ofthe segment 87 thus functioning as a micrometer spark gap for that particular sparking at the ignition gap. Interruption of the shorted magneto circuit occurs againwhen the leaf. 83 disengages the trailingedge of. thelower surface 88 of the segment 87, and this usually causes another discharge of the condenser. Thegapformed-in this instanceincreasesin 1'6 length very'slowly, because of the slow rotation of the cam and the lack of substantial drop of the leaf 83, and there is time for the buildup ofa charge on the condenser 23 to reach a value, less than the critical value, which will cause its discharge acrossthe slowly lengthening gap which, in this instance, acts as a micrometer spark gap. Starting of the engine at speeds as low as a very few revolutions per minute is thus effected without difliculty. Of course, at engine speeds greater than a. very few revolutions per minute the charge on tliecondenser 23 will reach its critical value and" the micrometer spark gap 21 will function in its normal manner. de scribed and there will be no tendency for discharge to occur at any time between the leaf 8'3 and the seg-, ment 87.

As already noted, the surface. of the contactingsegment 87 which is contacted by the end of the leaf. 83.

comprises both a portion of the surface of the camriser 84' and a portion 88 ofthe surface of'the cam body 85 itself. trailing edge of the riser 84 onto the surface. ofthe rotary member 85, it first contacts and follows the. conducting segment 87 again momentarily along its surface 88 before it begins to follow the non-conducting surface; of the rotary member 85. With the end of the leaf 83 in.

contact with the surface 88, the micrometer sparkgap. 21 is considerably longer than its. predetermined length and there is thus no possibility of sparking occurring across the gap. This momentarily recontacting of the. leaf 83 and the segment 87 with the gap 21 opened does, however, furnish an opportunity for the condenser 23-to' become completely discharged prior to its recharging;

by the next generated wave of the magneto current. The. importance of this is apparent when it is realized. that succeeding alternations in the magneto current are often.

denser completely of charges of one polarity before.

charging it with energy of the opposite polarity begins,

the maximum storage of energy in the condenser. 23. is.

achieved and the optimum operation of the ignition system is experienced.

It is noted that in the diagram of Figure 11 a secondv condenser 89, shown in dotted outline, is indicated. as being installed optionally across the magneto-circuit in, parallel with the micrometer spark gap 21. Such a condenser, which is entirely analogous in functiontothe condenser 31 of Figures 3 and 4, often. improvesthe character of the spark across the gap 21Tandserves as a reservoir of additional energy to increase the. intensity. of

the spark and the amount of high frequency current.

flowing in the primary coil 22.

In the modification illustrated in Figure. 12, threeleaf springs 92, 93 and 94, for convenience herein referred to as the upper, intermediate and lower leaves,. respectively, are provided with one end of' each. fixedv rigidly in an insulating support 47. The upper and intermediate leaves 92 and 93 support the facing electrodes 45 and 48, respectively, of the micrometer spark gap 21. An insulated adjusting screw 38 threadably engages the leaf 92 and bears on the leaf 93 to regulate the predetermined lengthof'the gap 21 at a suitable value. The

lower leaf 94--which extends beneath the leaf 93 is not" equipped'with an electrode and is insulated from the leaf 93 by a thin strip of insulating material-95 secured between them. The free end of the leaf 94 is engagedlby a cam riser 96. on: a rotary. cam .97.. havingan undercut- Thus, when the end'of the leaf 83 drops off the.

This becomes of special importance trailing edge 98. The riser 96 and the leaves 92, 93 and 94 are positioned with respect to one another so that when the end of the leaf 94 follows the surface of the cam riser 96 the leaf 94 presses the leaf 93 upward until it engages the end of the adjusting screw 38, thus estab lishing the micrometer spark gap 21 at its predetermined length. Any further movement of the leaf 94 upward in response to the urging of the cam riser 96 merely moves both the leaves 92 and 93 upward but does not alter the length of the micrometer spark gap 21. When the cam riser 96 disengages the end of the leaf 94, the latter drops downward and is followed by the leaf 93. The leaf 92 will also move downwardly to follow the leaf 93 through a portion of its travel but, if positioned and tensioned properly in the insulating block 47, does not tend to move downward through as great a distance as the leaf 92. Alternatively, an arresting member 90 can be employed to limit the movement of the leaf 92 downward, if desired, in a manner entirely similar to the employment of the arresting member 70 in the system of Figure 10. As a result of this cycle, the length of the micrometer spark gap 21 is increased from its predetermined length and thereby ventilated and purged and later reformed and stabilized at its predetermined length, it being understood that the rotation of the rotary member 97 is synchronized with the travel of the piston in an engine so that the micrometer spark gap 21 is always stabilized at its predetermined length prior to the time when the discharge of the condenser 23 is caused to take place across it.

The leaf 93 and the ungrounded terminal of the primary coil 22 are connected to one terminal of a magneto coil 27. The leaf 94 is also connected through a suitable switch 99 to the same terminal of the magneto coil. The leaf 92 and the rotary cam 97 and cam riser 96are connected to the other terminal of the magneto coil 27, generally through ground. The condenser 23, the primary coil 22 of the high frequency transformer and the micrometer spark gap 21 are thus connected in series in a high frequency primary circuit.

In operation, with the switch 99 closed, mechanical timing is obtained. The contacting of the free end of the leaf 94 with the cam riser 96 formsa shorted magneto circuit through the switch 99, the leaf 94 and the riser 96. When, however, the cam 96 disengages the end of the leaf 94, the shorted magneto circuit is interrupted, thus inducing a surge of high voltage current in the magneto coil 27 which charges the condenser 23 to its critical value causing it to discharge across the micrometer spark gap 21 before suflicient time has elapsed for the leaf 93 to drop out of contact with the adjusting screw 38 to lengthen the micrometer spark gap 21 beyond its predetermined length. This condition is facilitated by reason of the leaf 92 as well as the leaf 93 being moved upward in unison during the last stages of the upward travel of the leaf 94. The predetermined length of the micrometer spark gap 21 will thus be maintained for a certain portion of the time of downward travel of the leaf 93. Because of the dischargeof the condenser 23 across the gap 21, a high frequency oscillating current flows through the primary coil 22 generating a desired high frequency high tension current in the secondary coil 24 of the transformer causing sparking across the ignition gap 26. Further downward movement of the leaf 93 widens the gap 21 which, together with its subsequent return to its predetermined length, adequately cleans and ventilates the gap and reforms it in its stabilized condition. As the rotary member rotates further, the cam riser 96 again engages the end of the leaf 94. Complete discharge of residual charges on the condenser 23 is effected before generation of the next succeeding wave of opposite polarity begins.

The mechanical timing employing the mechanism of Figure 12 can be converted to wave-form timing by opening the switch 99. This can be done manually after the engine has attained satisfactory running speed or it can be controlled by the speed of the engine to provide for automatic switching from mechanical to completely waveformtiming at a predetermined engine speed. With the switch 99 open, current does not flow through the leaf 94 and no provision is made for forming and interrupting the shorted magneto circuit. The condenser is then charged directly by the magneto to its critical value, discharge occurs across the micrometer spark gap 21 and the circuit functions as previously described. However, with completely wave-form timing the cam riser 96 and the leaf 94 still function to alternately purge and ventilate the micrometer spark gap 21 and reform it in stabilized condition at its predetermined length.

Figures 13 and 14 illustrate schematically the applica tion of one modification of the ignition system of the invention to the ignition of a two-cycle outboard engine of a type having a flywheel mounted on the upper end of the crankshaft and consisting of a horizontal portion 162, as illustrated in Figure 14, from which depends a circular flange 103, the wheel being retained on the crankshaft 194 by a suitable retaining nut 105. A plate 106, herein referred to as an armature plate, is positioned coaxial with the crankshaft with its lower surface approximately flush with the lower edge of the flywheel flange 103. The wheel is generally of cast aluminum or other nonmagnetic metal and has one or more permanent magnets 1111) and corresponding pole shoes 107 embedded in the flange near its inner surface where the shoes pass close to a coil mounted on the upper side of the armature plate as the flywheel rotates. Provision is made for rotating the armature plate manually through an angle of several degrees to alter the timing of the ignition.

Figure 13 represents schematically a top sectional view of such an arrangement taken from just above the stationary armature plate 196 and showing how the conventional ignition system can be modified to convert it to one form of the system of the present invention. The flywheel flange 103 is shown in section and a permanent magnet and a pair of pole shoes 107 are shown embedded in the flange, the shoes, of course, being of opposite polarity. A suitable core 108 having a suitable magneto coil 109 wound on it is positioned on the armature plate 106 so that as the shoes 1117 move past it a current will be set up in it having a properly timed peaked voltage suitable for wave-form timing of the engine.

An insulating block 112 is secured to the armature plate 196 near its edge in any suitable manner, e.g. by a pair of screws 113. The insulating block 112 is cut away at one of its ends to leave a recess 122 and a protruding step 114 with its recessed surface facing the inside surface of the flywheel flange. The protruding step 114 is drilled horizontally to receive a bolt 115 for securing one electrode 116 of a micrometer spark gap 21 on the recessed surface. The other end of the insulating block 112 is drilled horizontally to receive a bolt 117 for securing one end of a leaf spring 113 to the side of the insulating block facing and in close proximity to the flywheel flange. The leaf spring 118 is tensioned in its mounting to rest near its free end on a suitable arresting member, such as a suitable projection 119 of the insulating block 112, which is located immediately adjacent the recess 122 formed in the end of the block. The free end of the leaf spring 118 projects over the recess 122 and has mounted on it an electrode 123 which, together with the electrode 116 which it faces, forms the micrometer spark gap 21. Another curved arresting member 124 is secured on the bolt 115 between the insulating block 112 and the nut 125 and extends to a point such that it contacts and prevents undue movement of the leaf 118 when the free end of the leaf moves away from the arresting member 119, as will be explained, so as to separate the electrodes 123 and 116. The arresting member 124 is formed of insulating material or is insulated from the leaf 118 in suitable manner, as by a pad of ini 19 sulating material 136 interposed between its free end and the leaf 118. The movement of the electrode 123 is, therefore, limited in'one direction by the projection 119 of the insulating block, which defines the predetermined length of the gap 21, and in the other direction by the end of the other arresting member 124.

The entire assembly of the insulating block 112 and its accompanying parts is located on the armature plate 106 so that, as the pole shoes 107 approach and move past it, the leaf 118, which is magnetically susceptible, is attracted toward the shoes and the electrodes 123 and 11.6 are separated from their predetermined distance to an extent which is limited by the arresting member 124. As the shoes 107 move on past the leaf 118, their attractive force for it decreases and the leaf 118 springs back into contact with the arresting projection 119 on the, insulating block 112. As the result of this sequence of operations, the micrometer spark gap 21 is widened so as to purge and ventilate it each time the flywheel revolves and is then immediately restored to its stabilized predetermined length before the shoes 107 approach and induce any appreciable current in the magneto coil 109.

One terminal of the magneto coil 109 is connected, e.g. by way of the bolt 117, to the insulated leaf 118 and the electrode 123. The other electrode 116 is connected, e.g. by way of the bolt 115, to the other terminal of the magneto coil 109, generally through ground. The ungrounded terminal of the magneto coil is also connected to one terminal of the primary coil 22 of a high frequency transformer secured on the armature plate, the other terminal of the primary coil 22 being grounded through a condenser 23. The primary coil 22, the micrometer spark gap 21 and the condenser 23 are thus connected in series in the primary high frequency circuit.

This arrangement provides for automatic Wave-form timing of the engine. As the shoes 107 move past the insulating block and its accompanying parts, the micrometer spark gap 21 is purged and ventilated and then reformed in a stabilized condition as described previously. The shoes 107, after leaving the vicinity of the insulating block 112, move past the magneto coil 109 carrying their magneticv field with them and setting up in the coil a peaked voltage current which charges the condenser 23 to its critical value such that it discharges across the micrometer spark gap 21. This sets up a high frequency oscillating current through the primary coil 22 which continues as long as the charge on the condenser 2.3 is sufficient to cause sparking across the ionized micrometer spark gap 21. A high frequency high tension oscillating current is set up in the secondary coil 24 of the transformer which causes sparking at the ignition spark gap 26, e.g. at the spark plug in the combustion chamber.

In the modification shown in Figure 13 it is apparent that sparking will occur at the ignition spark gap 26 once during each revolution of the flywheel. Inasmuch as most outboard engines operate on the two-cycle principle, the passage of the shoes 107 past the leaf 118 and the magneto coil 109 will be synchronized with the piston. No distributor will be necessary between the secondary coil 24 and the ignition gap 26 when a one-cylinder engine is involved. Furthermore, timing will be entirely automatic and adjusted to engine speed provided the magneto generates a current of suitably peaked voltage. In the event multiple cylinders are involved requiring firing at different times during the revolution of the flywheel, additional sets of magnets can be embedded in the flywheel and a suitable distributor can be installed in series with the ignition gap 26. It is apparent that the ignition cycle described will be repeated as many times during each revolution of the flywheel as there are sets of magnets and pole shoes to generate current impulses in the magneto coil 109. In the event two or more cylinders of the engine should 6d 0 fe at the same time, a corresponding number of additional sets of high frequency transformers and condensers can be connected in series or in parallel with the high frequency transformer and condenser shown, one set for each ignition spark gap. The currents generated in the secondary coils of the separate transformers will cause the respective ignition gaps to spark.

Provision can also be made in the ignition system just described to facilitate starting or slow speed operation of the engine by providing a pair of breaker points 126 and 127, one of which 127 is grounded and mounted on a flexible leaf spring and the other of which 126 is mounted on another leaf spring 129 which is insulated and connected through a suitable switch 128 to the ungrounded terminal of the magneto coil 109. One end of the flexihle leaf spring 129 is secured in an insulating block 132 on the plate 106'. The free end of the leaf 135 follows a suitably formed and timed cam surface 134, which can conveniently be formed on the crankshaft 104, in such a way as to form and interrupt a shorted magneto circuit as the crankshaft and flywheel revolve. With the switch 128 closed, sparking across the micrometer spark gap 21, and also across the ignition gap 26, will occur when the flywheel 103 is revolving at a speed much less than that required to charge the condenser 23 to its critical value directly with the magneto current.

Inasmuch as provision is generally made to rotate the armature plate 106 in such engines through a few degrees to regulate the timing, the same arrangement can be employed to regulate the mechanical timing during start ing and at low engine speeds, with the additional provision that when the timing is advanced to a certain degree by rotating the plate 106, the switch 128 is opened automatically and the timing thenbecomes entirely waveform in character.

The predetermined length of the micrometer spark gap 21 is controlled by the projection 119 of the insulating block 112. It is, of course, apparent that some wear of the end of the projection 119 will occur and that eventually the predetermined length of the micrometer spark gap 21 will decrease. This will cause premature firing of the engine after a long period of operation unless some means is provided for compensating for the Wear. One such convenient means, shown schematically in Figure 15, comprises an adjusting screw 38 passing through and threadably engaging the insulating block 112' and. thus providing an adjustable projection from the block against which the leaf 118 rests when the micrometer spark gap 21 is at its predetermined length. The entire insulating block 112, the leaf 118 and their accompanying parts can advantageously be enclosed in a tight aluminum, brass, plastic or other suitable non-magnetic housing to prevent as far as possible the access of dirt and other foreign material to the micrometer spark gap 21.

Inasmuch as access to the upper surface of the armature plate 106 necessitates the removal of the flywheel in the case of most outboard engines, it may sometimes be desirable to mount the insulating block 112 and its accompanying parts on the under side of the armature plate so that it can be renewed readily should the gap become irreparably fouled. This can be accomplished readily as shown schematically in Figure 14 by providing a pair of pole shoe extensions 133, one for each pole shoe of the, flywheel magnet, of laminated construction which are secured in and project through the armature plate. The upper end of each shoe extension is arranged so that its outer surface lies close to the inner surface of the flywheel flange 103 and so that the inner surface of its lower end lies close to the magnetically susceptible leaf 118. Under such conditions the magnetic flux will enter the shoe extensions 133 as the shoes. 107 move past their upper ends and will be transferred to their lower ends where it will exert almost as much attraction on the leaf spring 118 as would the magnets themselves with the leaf in the position shown in Figure 14. Using this arrangement it is convenient to supply the insulating block 112 and its accompanying parts in a totally enclosed plastic or brass case 134 with the micrometer spark gap 21 at a preset, nonadjustable, predetermined length. The case can be arranged to clamp onto the lower end of the shoe extensions 133 or onto any other suitable support secured to the plate 106 and the assembly can thus be renewed easily when need be.

In Figures 16, 17 and 18 there is shown a variation of the ignition system of Figure 13 insofar as the arrangement of the parts is concerned. In Figure 16 the armature plate 106, the flywheel flange 103, the magnet 100 and pole shoes 107 embedded in the flange are shown substantially as in Figure 13. In this instance, however, the micrometer spark gap, although easily replaceable, is located above the armature plate 106 where it is fully protected from mechanical injury, such as might sometimes happen in the arrangement of Figure 14. In the arrangement of Figure 16 the flux from the pole shoes 107 is concentrated, when the flywheel has revolved to bring the pole shoes to a suitable location, in a pair of poles 137 and 140 which are mounted in a fixed position on the armature plate 106 so that the pole shoes 107 pass close to their faces. A case 138 of nonmagnetic material and of suitable design open at its lower end is mounted, as will be explained, in a fixed position between the poles 137 and 140.

A laminated pole extension 139 is secured to the end of one of the poles 137 opposite the armature plate 106, herein referred to as the upper" end of the pole, in a position such that magnetic flux passes readily from the pole 137 into it. The pole extension 139 extends downwardly along the side of the non-magnetic case 138 to a position adjacent its open end. Another laminated pole extension 142 is secured to the upper end of the other pole 140 in a position such that magnetic flux passes into it readily from the pole 140. The pole extension 142 extends to a position adjacent the wall of the non-magnetic case 138 and terminates at a location which will be indicated later. The non-magnetic case 138 is conveniently secured to the pole extensions 139 and 142, as by a suitable bracket 120 and a screw 121, respectively.

A plug 143 made of a suitable insulating material, e.g. of a synthetic resin, is formed so that it will slide snugly into the open end of the case 138. The bottom of the plug 143 is formed to seat on a removable laminated support 144 which, in its normal position, has one end closely adjacent or in laminating contact with the lower end of the pole extension 139 to provide for free flow of magnetic flux between them. The laminated support 144 extends across the bottom of the insulating plug 143 away from the end of the pole extension 139 and has an upturned end section 148 which extends for a suitable distance up the opposite side of the plug 143. The insulating plug 143 and the laminated member 144 are held in place in the case 138 by any suitable arrangement adapted to their removal when desired. One such arrangement includes a spring 145 secured to swing laterally on the under side of the armature plate 106 as by a screw 146. The spring 145 is conformed at its free end to engage the lower side of the laminated support 144 or a suitable depending extension 147 thereof. Suitable provision is made to insure the proper angular location of the plug 143 in the case 138, conveniently by making them both with rectangular cross sections.

When it is desired to exchange the insulating plug 143 on which the micrometer spark gap is mounted, as will be explained subsequently, for a new one, the spring 145 is disengaged from the extension 147 or the laminated support 144 and the insulating plug 143 can then be withdrawn from the case 138 and a new unit carrying a new micrometer spark gap inserted.

The insulating plug 143 is cut away on the side adjacent the pole extension 142 to form a groove into the lower end of which the upwardly turned end 148 of the laminated support 144 extends. The upper end of the groove is formed as a suitable leaf-arresting projection 149. Above the leaf-arresting projection 149 the plug is cut away further to form a recess 152. A leaf spring 153 is secured to the upturned end 148 of the laminated support 144, e.g. by a screw 154 which passes through the leaf 153 and upturned end 148 of the laminated support 144 and engages the insulating block threadably, thus securing them firmly together as a unit. The leaf 153 has an electrode 116 secured at its upper end facing into the recess 152.

Another electrode 123 which, together with the electrode 116, forms the micrometer spark gap 21, is mounted, preferably adjustably, at the bottom of the recess 152 facing the electrode 116. The electrode 123 can conveniently be secured to the end of a bolt 155 which engages the upper end of the insulating block 143 threadably and which can be locked in place by means of a nut 156, a spring contacting member 157 being secured under the nut 156. Adjustment of the length of the micrometer spark gap 21 is effected by rotating the bolt 155 in the block 143 until, with the leaf 153 resting on the arresting projection 149, the gap 21 is at its predetermined length.

The spring contacting member 157 projects upward above the top of the insulating block and is positioned so that, with the insulating block 143 in its proper location, it contacts the end of a terminal member 159. The terminal member 159 extends through the wall of the case 138, being insulated therefrom by an insulating bushing 162 and held firmly in place by a suitable nut 163. An insulating conducting path is thus provided from the electrode 123 to the terminal 159.

The end of the terminal member 159 is connected to the ungrounded terminal of the magneto coil and to the ungrounded terminal of the primary coil of the high frequency transformer. The eletrode 116 and the leaf 153 are grounded in any suitable way, e.g. through the laminated support 144, the extension thereof 147 and the retaining spring to the armature plate 106. The pole extensions 139 and 142 are generally grounded by reason of the manner in which they are mounted. The micrometer spark gap 21 is thus connected in series wtih the condenser and the primary coil of the transformer in the primary high frequency circuit in the manner heretofore described.

The upper end of the pole extension 142 extends along the side of the case 138 to a point approximately opposite the upper end of the leaf 153, thus furnishing a maximum opportunity for the flow of magnetic flux from the upper end of the leaf 153 into the pole extension 142 through the non-magnetic wall of the case 138. Thus when the poles 137 and 141 are energized by the proximity of the pole shoes 1117 there is an efficient conduction of the magentic flux from the pole 137 through the pole extension 139, the laminated support 144, the leaf 153, through the wall of the non-magnetic case 138 to the other pole extension 142 and through the pole 146. The upper end of the leaf spring 153 is thus attracted strongly to the pole extension 142 and the length of the micrometer spark gap 21 is thereby increased and the gap is cleaned and ventilated. When the pole shoes 107 recede from the faces of the poles 137 and 140, the attraction of the leaf 153 to the pole extension 142 ceases and it springs back into contact with the leaf arresting projection 149. The micrometer spark gap 21 is thus reestablished at its predetermined length and the operation of the ignition system proceeds as in the manner described in Figure 13.

1 Although the invention has been descibed from the point of view of the micrometer spark gap being stabilized at its predetermined length prior to and during the time at which the charge on the condenser 23 reaches and it at its critical value and from the point of View of the ventilation and purging of the gap occurring at some time between the recurrence of two such consecutive charges on the condenser, it is pointed out that it is sometimes advisable to place further restrictions on the variation in length of the micrometer spark gap. It is known that certain types of magnetos, for example, produce a current having a voltage of more or less complex wave form and that in certain instances the voltage produced is adequate to charge the condenser to its critical value at times when its discharge across the micrometer spark gap would be undesirable. In addition, when the ignition system of the invention is used on a two-cycle engine and the magneto is mounted on the crankshaft, it is apparent that it will be undesirable for discharge of the condenser 23 across the micrometer spark gap 21 to occur during each increase in voltage of the magneto current. In other words, it will be desirable in such instances for the ignition system to be non-functional during certain portions of the generated wave-form cycle, especially since the functioning of the system is independent of the polarity of the increasing voltage. For this reason, the means for purging and ventilating the micrometer .spark gap can often be arranged with advantage to hold the length of the gap at a value greater than the predetermined length during certain parts of, or during a major proportion of, the time when it is not required to be at its predetermined length. In this way the resistance of the micrometer sprak gap to discharge of the condenser across it is maintained at a value so great that no danger of such unwanted discharge exists, it being understood, of course, that the gap is restored to its predetermined length in ample time for it to become stabilized prior to the attainment of the critical charge on the condenser at the time in the cycle that functioning of the ignition system is desired. Such provisions, which are contemplated by the invention, can be incorporated in the system in any desirable way, either by employing separate magnetic or mechanical means or by suitable modification of the means for varying the length of the micrometer spark gap already described, to regulate positively the length of the micrometer spark gap during that part of the time when its functioning at its predetermined length is undesired.

It has been pointed out, and is reiterated here, that the ignition system of the invention provides for an ignition spark of extremely long duration as compared with the duration of the ignition spark provided by most other more conventional systems. As a matter of fact, the duration of the ignition spark, especially at high engine speeds, is sometimes so long, due to the wave form of the current generated by certain types of magnetos and to the persistence of the discharge across the ionized gap, that it is desirable to interrupt or quench it before it would otherwise normally cease. This can be accomplished by suitable adaptation of the mechanical or magnetic means referred to in the preceding paragraph for preventing discharge of the condenser across the micrometer spark gap at unwanted intervals. The

invention thus provides an ignition system in which not only are the advantages heretofore pointed out inherent but also in which the duration of the ignition spark can be limited, as desired, and in which the occurrence of a spark at the ignition spark gap at unwanted times can be prevented easily.

Although the system described is of particular value in the ignition of internal combustion engines, it is pointed out that it can be used in any application where high frequency, high tension sparking across a spark gap at regulated intervals is desired. Such other uses in- 24 eludes the operation of fuel igniting apparatus, X-ray machines and the like.

I claim:

1. In an electrical system, the combination including: a condenser, a micrometer spark gap and a primary coil of a high frequency transformer connected in series in a high frequency primary circuit; and a source of current of cyclically increasing voltage for charging the condenser intermittently to a critical value sufiicient to cause its discharge across the micrometer spark gap and the flow of a high frequency oscillating current in the primary coil, the micrometer spark gap having electrodes with substantially parallel facing surfaces spaced aocurately at a predetermined distance from one another immediately prior to and during each interval of discharge of the condenser but varying from the predetermined distance during at least a portion of each voltage cycle when the condenser charge is below the critical value.

2. In an electrical system, the combination including: a condenser, a micrometer spark gap and a primary coil of a high frequency transformer connected in series in a high frequency primary circuit, the micrometer spark gap having electrodes with parallel facing surfaces; means to vary the length of the micrometer spark gap cyclically from a predetermined length; and a source of current of cyclically increasing voltage for charging the condenser at regular intervals to a critical value sufficient to cause its discharge across the micrometer spark gap when the gap is of the predetermined length, the micrometer spark gap length being synchronized with the voltage wave of the current to insure the gap being at its predetermined length immediately prior to and during an interval of a voltage cycle when the charge on the condenser is at the critical value, but varying from its predetermined length during at least a portion of a voltage cycle when the charge on the condenser is below the critical value.

3. The combination as claimed in claim 2 wherein the means to vary the length of the micrometer spark gap is a mechanical means.

4. The combination as claimed in claim 2 wherein the means to vary the length of the micrometer spark gap is a magnetic means.

5. The combination as claimed in claim 2 wherein the length of the micrometer spark gap becomes less than its predetermined length during at least a portion of each voltage cycle when the charge on the condenser is below the critical value.

6. The combination as claimed in claim 2 wherein the length of the micrometer spark gap becomes less than its predetermined length and the electrodes forming the gap contact one another during at least a portion of each voltage cycle when the charge on the condenser is below the critical value.

7. The combination as claimed in claim 2 wherein the length of the micrometer spark gap becomes greater than its predetermined length during at least a portion of each voltage cycle when the charge on the condenser is below the critical value.

8. The combination as claimed in claim 2 wherein the electrical system is an ignition system for an internal combustion engine and the voltage of the current has a wave form suitable for wave-form timing of the engine.

9. In an electrical ignition system for an internal combustion engine, the combination including: a magneto as the source of a current of cyclically increasing voltage having a wave form suitable for wave-form timing; a micrometer spark gap varying cyclically in length from a predetermined length; a condenser; a high frequency transformer; and an ignition spark gap in the combustion chamber of an engine, the ignition spark gap, the second aty coil of the transformer and the condenser being connected in series in a secondary high frequency circuit, the micrometer spark gap, the primary coil of the transformer and the condenser being connected in series in a primary high frequency circuit energized by the magneto and the magneto, the primary coil of the transformer and the condenser being connected in series in a magneto circuit; and synchronizing means to assure the micrometer spark gap being at the predetermined length immediately prior to and during an interval when the condenser is charged at its critical value sufiicient to cause its discharge across the micrometer spark gap at the predetermined length.

10. A combination as claimed in claim 9 wherein the micrometer spark gap is in parallel in the magneto circuit with the primary coil of the transformer and the condenser.

11. In an electrical ignition system for an internal combustion engine, the combination including: a magneto as the source of a current of cyclically increasing voltage having a wave form suitable for Wave-form timing of the engine ignition at moderate and high engine speeds; a micrometer spark gap variable cyclically in length from a predetermined length; condenser, a high frequency transformer; an ignition spark gap in the combustion chamber of an engine, the ignition spark gap, the secondary coil of the transformer and the condenser being connected in series in a secondary high frequency circuit,

.the micrometer spark gap, the primary coil of the transformer and the condenser being connected in series in a primary high frequency circuit energized by the magneto and the magneto, the primary coil of the transformer and ,the condenser being connected in series in a magneto circuit; circuit-forming and interrupting means connected directly across the magneto circuit in parallel with the magneto coil for forming and interrupting a shorted magneto circuit at low engine speeds to provide a surge of high voltage current from the magneto coil, the voltage wave of the magneto current, the circuit-forming and interrupting means and the variance in length of the micrometer spark gap being synchronized to assure the micrometer spark gap being at the predetermined length immediately prior to and during an interval when the condenser is charged at its critical value sufficient to cause its discharge across the micrometer spark gap at the predetermined length.

12. A combination as claimed in claim 11 wherein the circuit-forming and interrupting means becomes operative automatically at low engine speeds when the voltage of the magneto current at the peak of its wave is insufficient to charge the condenser to its critical value and inoperative automatically at moderate and high engine speeds when the voltage of the magneto current is sufficient to charge the condenser to its critical value and effect automatic wave-form timing.

13. In a high frequency ignition system for an internal combustion engine employing a magneto circuit and adapted to effect automatic wave-form timing of the engine at moderate and high engine speeds and to effect make and break timing at low engine speeds and during starting, the combination including: a flexible leaf spring secured at one end in an insulating mounting and having a first electrode secured at its opposite end; a second electrode mounted in a fixed position and, together with the first electrode, forming a micrometer spark gap connected in series in a primary high frequency 7 circuit with the primary coil of a high frequency transformer and a condenser, the tension of the leaf spring urging the first electrode away from the second electrode to increase the length of the micrometer spark gap; adjustable means to limit the increase in length of the micrometer spark gap to a predetermined length; and magnetic means operable periodically on the leaf spring to shorten the micrometer spark gap and, at low engine speeds, to cause the first electrode alternately to contact and to separate from the second electrode, the elecrodes then functioning as a circuit-forming and interrupting means connected directly across the magneto circuit for forming and interrupting a shorted magneto circuit.

starting, the combination including: upper and lower leaf springs, each secured rigidly at one end in an insulating mounting, having upper and lower electrodes secured adjacent their respective opposite ends forming a mirometer spark gap connected in series in a primary high frequency circuit with the primary coil of a high frequency transformer and a condenser, the tension of the springs urging the electrodes toward one another to decrease the length of the micrometer spark gap; adjustable ,means associated with the lower leaf spring and insulated from the upper leaf spring to limit the decrease in length of the micrometer spark gap to a predetermined length; a rotary cam having a cam riser adapted alternately to engage the upper leaf spring and increase the length of ,the micrometer spark gap and to disengage the upper leaf spring, the cam riser and the upper leaf spring functioning as a circuit-forming and interrupting means ,connected directly across the magneto circuit for forming and interrupting a shorted magneto circuit; and switch means to render the shorted magneto circuit ineffective at moderate and high engine speeds.

16. In a high frequency ignition system for an internal combustion engine employing a magneto circuit and adapted to effect make and break timing, the combination including: upper and lower leaf springs, each secured at one end in an insulating mounting, having upper ,and lower electrodes secured adjacent their opposite ends,

the two electrodes forming a micrometer spark gap connected in series in a primary high frequency circuit with the primary coil of a high frequency transformer and a condenser, the tension of the lower leaf spring urging the lower electrode away from the upper electrode to lengthen the micrometer spark gap; adjustable means to limit the increase in length of the micrometer spark gap to a predetermined length; a rotary cam having a cam riser adapted alternately to engage and lift and to disengage the lower leaf spring to cause the lower electrode alternately to contact and to disengage the upper electrode, the two electrodes functioning, additionally, as a circuit forming and interrupting means connected across the magneto circuit for forming and interrupting a shorted magneto circuit.

17. In a high frequency ignition system for an internal combustion engine employing a magneto circuit and adapted to effect automatic wave-form timing of the engine at moderate and high engine speeds and to effect make and break timing at low engine speeds and during starting, the combination including: upper and lower leaf springs, each secured at one end in an insulating mounting, having upper and lower electrodes secured adjacent their opposite ends forming a micrometer spark gap connected in series in a primary high frequency circuit with the primary coil of a high frequency transformer and a condenser, the tension of the lower leaf spring urging the lower electrode away from the upper electrode to lengthen the micrometer spark gap; a rotary cam having a cam riser adapted alternately to engage the lower leaf spring and urge the lower electrode toward the upper electrode to shorten the micrometer spark gap and to disengage the lower leaf spring; adjustable means asso ciated with the upper leaf spring and insulated from the lower leaf spring to prevent shortening of the micromface of the rotary cam including the trailing edge of the cam riser and adjoining sections of the cam surface on each side thereof, the conducting segment and the lower leaf spring functioning at low engine speeds as a circuitforming and interrupting means connected across the magneto circuit to alternately form and interrupt a shorted magneto circuit.

18. In a high frequency ignition system for an engine employing a magneto current generated in a magneto coil located closely adjacent the path of magnet pole shoes rotating with the engine crank shaft and adapted to supply current suitable for effecting automatic waveform timing of the engine, the combination including: an insulating block mounted in fixed position adjacent the path of the rotating pole shoes; a first electrode mounted on the insulating block; a leaf spring mounted at one end on the insulating block adjacent the path of the rotating pole shoes and having a second electrode secured at its other end facing the first electrode and forming therewith a micrometer spark gap connected in series in a primary high frequency circuit with the pri mary coil of a high frequency transformer and a condenser, the leaf spring being tensioned to urge the second electrode toward the first electrode to shorten the micrometer spark gap and being adapted to be attracted and to flex toward the passing pole shoes to urge the second electrode away from the first electrode to lengthen the micrometer spark gap; and means to limit the decrease in length of the micrometer spark gap to a predetermined length.

19. In a high frequency ignition system for an engine employing a magneto current generated in a magneto coil located on an armature plate closely adjacent the path of magnet pole shoes rotating with the engine crank shaft and adapted to effect automatic wave-form timing of the engine at moderate and high engine speeds and to effect make and break timing at low engine speeds and during starting, the combination ineluding: an insulating block mounted on the armature plate adjacent the path of the rotating pole shoes; 21 first electrode mounted on the insulating block; a leaf spring mounted at one end on the side of the insulating block adjacent the path of the rotating pole shoes and having a second electrode secured at its other end facing the first electrode and forming therewith a micrometer spark gap connected in series in a primary high frequency circuit with the primary coil of a high frequency transformer and a condenser, the leaf spring being tensioned to urge the second electrode toward the first electrode to shorten the micrometer spark gap and being adapted to be attracted and flexed toward the passing pole shoes to urge the second electrode away from the first electrode to lengthen the micrometer spark gap; means to limit the decrease in length of the micrometer spark gap to a predetermined length; cam actuated circuit-forming and interrupting means mounted on the armature plate and connected across the magneto circuit to alternately form and interrupt a shorted magneto circuit; and switch means to render the shorted magneto circuit ineffective at moderate and high engine speeds.

20. In a high frequency ignition system for an engine employing a magneto current generated in a magneto coil located closely adjacent the path of magnet pole shoes rotating with the engine crankshaft and adapted to effect automatic wave-form timing of the engine at moderate and high engine speeds and to effect make and break timing at low engine speeds and during starting, the combination including: an insulating block mounted in fixed position adjacent the path of the rotating pole shoes; a first electrode mounted on the insulat ing block; a leaf spring mounted at one end on the side of the insulating block adjacent the path of the rotating pole shoes and having a second electrode secured at its other end facing the first electrode and forming therewith a micrometer spark gap connected in series in a primary high frequency circuit with the primary coil of a high frequency transformer and a condenser, the leaf spring being tensioned to urge the second elec trode toward the first electrode to shorten the micrometer spark gap and being adapted to be attracted and flexed toward the passing pole shoes to urge the second electrode away from the first electrode to lengthen the micrometer spark gap; means to limit the decrease in length of the micrometer spark gap to a predetermined length; cam actuated circuit-forming and interrupting means connected across the magneto circuit to alternately form and interrupt a shorted magneto circuit; and switch means to render the shorted magneto circuit ineffective at moderate and high engine speeds.

21. In a high frequency ignition system for an outboard engine employing a magneto circuit for a magneto current generated in a magneto coil mounted on an armature plate closely adjacent the path of rotating magnet pole shoes embedded in the engine flywheel mounted on the engine crankshaft, and adapted to effect automatic wave-form timing of the engine at moderate and high engine speeds and to effect make and break timing at low engine speeds and during starting, the combination including: an insulating block mounted on the armature plate adjacent the path of the rotating pole shoes; a first electrode mounted on the insulating block; a leaf spring mounted at one end on the side of the insulating block adjacent the path of the rotating pole shoes and having a second electrode secured at its other end facing the first electrode and forming therewith a micrometer spark gap connected in series in a primary high frequency circuit with the primary coil of a high frequency transformer and a condenser, the leaf spring being tensioned to urge the second electrode toward the first electrode to shorten the micrometer spark gap and being adapted to be attracted and flexed toward the passing pole shoes to urge the second electrode away from the first electrode to lengthen the micrometer spark gap; means to limit the decrease in length of the micrometer spark gap to a predetermined length; cam actuated circuit-forming and interrupting means mounted on the armature plate and connected across the magneto circuit to alternately form and interrupt a shorted magneto circuit; and switch means to render the shorted magneto circuit ineffective at moderate and high engine speeds.

22. In an electrical ignition system for an internal combustion engine having an ignition spark gap in the combustion chamber of the engine in series with the secondary coil of a high frequency transformer and a magneto supplying current having voltage wave-form characteristics suitable for automatic wave-form timing to the primary coil of the transformer, the combination including: a micrometer spark gap having electrodes with parallel facing surfaces connected in series with a condenser and the primary coil of the high frequency transformer in a high frequency primary circuit; and means to vary the distance of the electrodes from one another while maintaining their surfaces essentially parallel after one discharge of the condenser across the gap and for returning the electrodes to a predetermined distance from one another to form a stabilized gap of predetermined length prior to the accumulation of a charge on the condenser sufficient to cause it to discharge again across the stabilized gap.

Holthouse Nov. 3, 1936 Holthouse June 25, 1940 

